KABUL (Reuters) - At a dinner party in Kabul's high-security "green zone" in March, a senior European diplomat poured himself a glass of red wine and pulled up a photograph on his iPhone.

Released by Qatar's foreign ministry on Feb. 25, it showed seven Qatari officials alongside U.S. and Taliban negotiators as talks on ending the 17-year-old war in Afghanistan had restarted in the Gulf state the previous day.

"If Qatari officials can be at the negotiating table, then how did the U.S. forget to invite its key allies who have fought the Afghan war since 2001?" said the diplomat, whose nation has contributed hundreds of troops to NATO's mission in the country.

"We continue to pour millions of dollars as an act of solidarity, but when it comes to peace talks, the U.S. decided to go solo."

Reuters spoke with 10 diplomats from countries spanning three continents that are among the 39 that provide military personnel to the NATO training operation, known as Resolute Support, in Afghanistan, and those that provide development aid.

Many of those countries are significant, consistent donors. Most of the diplomats spoke on condition of anonymity, citing the sensitivity of the situation.

The diplomats interviewed said their governments were broadly rethinking their commitments to rebuilding the country. That process had been hastened by feeling excluded from peace talks, and also by a weariness for supporting the Afghan campaign among voters and lawmakers in their respective countries, they said.

Asked about those comments, a U.S. State Department spokesperson said regular reviews of foreign assistance was "good practice" and Afghanistan's development remained in the interest of the international community.

"We see no signs that interest and investment are wavering," said the spokesperson, adding that U.S. Special Representative Zalmay Khalilzad has briefed NATO allies and other partners three times since December, and effective coordination remained a priority.

But even the Afghan government has complained of being left out. President Ashraf Ghani's national security adviser on Thursday accused Khalilzad of "delegitimising" the Kabul government by excluding it from deliberations.

Qatari officials did not respond to a request for comment.

In 2017, U.S. development aid for Afghanistan totalled about $1.2 billion, well ahead of the next biggest donors Germany, European Union institutions, Britain and Japan, according to Organisation for Economic Co-operation and Development (OECD) data. But the United States' junior aid partners collectively contributed nearly two-thirds of all development assistance, highlighting their critical if less visible importance to the country's future.

CHANGING PRIORITIES

U.S. and Taliban negotiators wrapped up their longest round of peace talks on Tuesday with progress made but no agreement on when foreign troops might withdraw.

Whether funding countries keep investing in Afghanistan could prove pivotal to sustaining any peace. Diplomats say that, after troops leave, it may be the only leverage they have to retain influence over future Afghan governments.

Since the 2001 U.S.-led invasion, Afghanistan has been among the top recipients of foreign government aid to promote economic and social development. In 2016, international donors pledged $15.2 billion in aid for Afghanistan until 2020.

With those pledges due to expire, many countries are re-evaluating their military and funding commitments.

"Priorities have changed for every EU nation," a European diplomat said, adding that countries besides Afghanistan needed support.

"The donor fatigue is intense and no one is in the mood to overlook it after 2020," another diplomat said.

A third diplomat said their country was re-evaluating its future aid with different scenarios in mind, including whether to continue development if the Taliban joins Afghanistan's government, and what to do if peace talks fail.

Any drop-off in international aid would be disastrous for Afghanistan, since much of it funds basic health and education services, said Adele Khodr, country representative for Unicef.

"It is definitely something we are concerned about. Imagine what would happen - (Afghanistan) would be Yemen," Khodr said. "(By) pulling out, the international community will pay a much higher price in insecurity across the world."

Ninety percent of the money spent on the health sector in Afghanistan comes from the international community, said Toby Lanzer, deputy special representative in Afghanistan for the UN.

An official in Ghani's office in Kabul declined to comment on potential risks to future aid.

He said the government was making every effort to hold peace talks with the Taliban. The militant group said on Tuesday that such talks would have to wait until after a troop withdrawal plan is set.

'CRUCIAL TO STICK TOGETHER'

Some diplomats caution against a quick retreat.

"If we leave the country hastily, all these (advances) will go down the drain," Ambassador Markus Potzel, Germany's special representative for Afghanistan and Pakistan and one of the 10 diplomats interviewed, told Reuters in Kabul.

Potzel was referring to gains such as Afghan girls' attendance in school and new employment opportunities.

Maintaining aid was also critical to holding influence in Afghanistan, he said.

A spokesperson at the British Embassy in Kabul said any changes to Britain's troop contribution would be made in consultation with coalition partners.

As of March 2019, 39 countries contributed 17,034 foreign forces in Afghanistan for Resolute Support, of which the U.S. provided 50 percent, according to NATO. U.S. troops are also deployed in a separate mission directed against groups such as al Qaeda and Islamic State.

U.S. President Donald Trump's questioning of NATO's value to Washington, along with the absence of allies at the negotiating table, has deepened the unease within the military alliance created in 1949 by the United States, Canada, and Western European nations.

"The concern is that we need to be appraised of the progress of the discussions and to be involved. We have invested a lot," said a European diplomat. "This commitment should be reflected in influence or at least information on the peace talks."

The diplomat said it was understandable that access to the negotiating table was narrow right now, but "what I would find abnormal is that we would be served a deal in which we had nothing to say and then be asked to foot the bill".

SHRINKING FOOTPRINT?

The senior diplomats interviewed by Reuters, who are based in Kabul and Islamabad, said their governments were finding it harder to justify the continuing presence of their troops and the steady drain of aid funding to Afghanistan.

"It is increasingly difficult to tell our people why we are still here especially when they read reports about more than half of country being under the Taliban control," said a Western diplomat. "Almost all NATO countries are now struggling to justify their presence in Afghanistan to voters back home."

The war's long duration has also weakened commitment.

"If we had known that the war could go on as it has been for 18 years, we would have had a rethink in 2001," the Western diplomat said.

The withdrawal of foreign troops from Afghanistan has always been the Taliban's main demand, and Trump's interest in drawing down U.S. troops has stimulated efforts to end the war.

"The prime concern is that we may wake up one day to a tweet by Trump about a unilateral withdrawal of U.S. troops before a peace agreement has been negotiated," said a diplomat whose country supports Afghan healthcare projects.